The present invention is directed to coating compositions for use as decorative finish or top coats for automobile vehicle bodies.
In the automotive industry two significant systems are utilized in the painting of automobiles. One topcoat system which utilizes thermoplastic resins is known as the acrylic lacquer system. The other topcoat system used in the automotive industry is the thermosetting acrylic resin as described in U.S. Pat. No. 3,375,227, issued May 26, 1968.
Because of environmental considerations, organic solvent reducible acrylic enamels of the foregoing type have been superseded in certain situations by water reducible acrylic enamels.
Multilayer coating systems are also well known in the coating industry. These coating systems which comprise a thin aluminum flake pigmented base coat and a clear top coat are increasingly popular in the automotive industry. The majority of cars manufactured in Europe and Japan are painted with base coat-clear coat systems. The advantages of the base coat-clear coat multilayer coating system are numerous including outstanding appearance, superior gloss, improved chemical and mar resistance, and extended duty. In order to prepare these systems it has been required that each coat be baked or cured before a second or topcoat is applied. Thus several time consuming baking or curing steps are normally required where multilayer systems are applied. In U.S. Pat. No. 3,639,147 a multilayer coating system is described that eliminates the need to bake or cure the base layer before the second or topcoat is applied. This multilayer coating system has been adapted by the original equipment paint industry.
Repairing the base coat-clear coat finishes in the field has represented a problem. As previously mentioned, the multilayer coatings used by the OEM manufacturers must be baked in order to be useful. Repair shops require a base coat-clear coat refinish coating system which is capable of being dried in ambient room air. In addition, this refinish coating must match the characteristics of the OEM coating.
This invention relates to the use of chlorinated polyolefins in a coating containing a metallic flake pigment thereby preventing metal flake disorientation. This invention further relates to a base coat-clear coat which can be applied in the field and dried under ambient room air conditions resulting in an applied coating which matches the OEM coating, wherein the basecoat contains chlorinated polyolefins. This invention is also applicable to base coat - clear coat OEM baked coatings.
An advantage of this invention is that it permits the use of increased pigment concentrations in the base coat or top coat resulting in a thinner applied coating.
The prior art contains several examples of polymeric coating compositions useful for refinishing or repairing damaged coatings in the field. An acrylic coating composition for refinishing flexible automobile and truck bumpers is shown in Sheppard U.S. Pat. No. 3,829,397 issued on Aug. 13, 1974 and U.S. Pat. No. 3,893,960 issued on July 8, 1975.
A water-based alkyd resin coating composition is shown in Miller U.S. Pat. No. 4,321,169 issued on Mar. 23, 1982. The coating composition disclosed in Miller can be dried at ambient temperatures and is useful for coating metal and plastic substrates and in particular for finishing or repairing automobiles and trucks.
A acrylic coating composition for repairing acrylic lacquer coatings which are used in the auto industry is disclosed in Willey U.S. Pat. No. 3,711,411 issued on Jan. 16, 1973.
The disclosures of U.S. Pat. Nos. 3,829,397; 3,893,960; 4,321,169 and 3,711,411 are incorporated by reference.
Aesthetically, the acceptable appearance of a metallic pigmented coating is dependent upon the correct orientation of the metal particles. The acceptable appearance of a metalized coating is defined as that appearance which usually matches the appearances of a reference standard, or, if no such standard exists, the coating should exhibit a surface free from mottling, ghosting, general discontinuities, or any visual apparation signifying disorientation of the included metal.
The formulation of metallic coatings generally is limited to small amounts of included metallic pigment. Usually, metallic pigments in excess of 3% of the coating composition will lead to metal disorientation characterized by application problems resulting in the loss of an acceptable appearance.
In order to completely hide or cover the surface to be coated, repeated applications of the coating are required, often resulting in an excessively thick film. Excessively thick films are characterized by film embrittlement and general loss of adhesion and flexibility. Film thickness exceeding 2-2.5 mils are considered undesirable. A mil is defined as 0.001 inches.
Excessive film thickness is particularly prevalent when the metallic color coat is overlaid with a clear transparent coating designed to enhance gloss, durability and general aesthetics.
When applying a clear overlay over a metallized basecoat, the desired film thickness can be achieved by applying a very thin layer of the basecoat, followed by a normal thickness application of the clear coat. In order to achieve complete hiding by the basecoat, more metallic pigment must be included in its composition without detriment to its appearance. Increased amounts of metallic pigment can be incorporated into the coating by introducing adjunct binder materials. These adjunct materials are characterized by a general lack of color, and an ability to protect the metal particles from disorientation during application. Such adjunct binders are currently employed by the industry. An example is a copolymer of polyethylene and vinyl acetate manufactured by Allied Chemical Corporation and designated as AC405. Other examples are a number of commercially available non aqueous acrylic resin dispersions as in U.S. Pat. No. 4,220,679.
Ideally, an adjunct binder suitable for protecting metal flakes from disorientation during application: (1) should be uneffected by the presence of companion binders, (2) should not be influenced by the solvent combination employed in the coating formulation; (3) should not detract from the achievement of a desired color; and, (4) should be easily incorporated into any coating composition containing metal flakes using standard mixing procedures. Chlorinated polyolefins meet the previously stated requirements.
The problems and disadvantages associated with prior art base coat-clear coat refinish paint systems are overcome in accordance with the present invention wherein the addition of a chlorinated polyolefin resin to the base coat results in the metal fixation needed for proper color match and appearance.